In general, in an internal combustion engine such as a reciprocating or piston engine or a rotary engine, an ignition point of the engine has been controlled so that a desired advance characteristics can be obtained in response to the revolution speed of the engine. By way of example, since the reciprocating engine has the relatively lower motion speed of the piston when it is started and also since gas leakage occurs between the piston and the cylinder when it is started, the inner pressure in the cylinder tends to have the highest value at the point before the piston reaches the upper dead point while the crank of the engine is rotating. Accordingly, if the engine is ignited at the point of the piston when the inner pressure in the cylinder has the highest value, the most preferable starting characteristics can be obtained, which is well known in the art. The point of the piston when the inner pressure has the highest value on initiation depends on the speed of rotation of the crank and the condition of the gas leakage. Generally, it is at the angle of 10.degree. to 15.degree. prior to the upper dead point of the piston. After the engine is started, the point of the piston when the inner pressure in the cylinder has the highest value is at the angle of 5.degree. to 7.degree. on idling of the engine because the speed of rotation of the crank increases and because the gas leakage decreases. In the event that load is applied to the engine during high speed rotation thereof, it is required to be ignited at the point of 30.degree. to 50.degree. prior to the upper dead point so that the ignition point is advanced because if otherwise combustion cannot follow the motion of the piston.
A conventional ignition system comprises a governor adapted to angularly shift a contact breaker about a cam shaft so that the ignition point is advanced in phase with increasing speed. The advance characteristic provided by such conventional ignition system is as indicated by the dotted line in FIG. 1. If the governor is designed so that on starting of the engine the ignition point is advanced, then it has a complicated construction and therefore, the desired starting characteristics cannot be practically employed.
A breakerless ignition system to which the present invention is directed has not provided such desired starting characteristics because it is difficult that it is designed in such a manner.